Space Elevator

One application of centripetal force and circular motion is found in the space elevator lift. It was proposed by Russian scientist, Yuri Artsutanov in 1960 as a possible way of getting into space. It works on the principle that at a object orbiting the Earth above the equator with a period of 24 hours will remain in the same position above the Earth (see geostationary satelites).

If a rope were to be lowered from the object, then an elevator car could climb up the rope into space without the need for a rocket. Since the rope has mass the additional weight of the rope would cause the satellite holding it to be pulled back to Earth. However, a counter weight orbiting the Earth a greater distance than the geostationary height would be travelling faster to stay in the same position over the equator the centripetal force of the counterweight can be balanced against the weight of the rope. The result is that the rope stays in place and the space elevator becomes possible.

Even though the theory is sound, there are significant technical challenges yet to be overcome before the space lift becomes a reality. The first is to do with the material properties of the rope. Given that the height of the geostationary orbit is some 3.58 x 10⁴ km above the equator, any rope would have to be extremely strong to support its own weight. At present there is no known material that would be able to support its own mass at this length however, carbon-nanotubes have been suggested as a possible material for such ropes because of their low mass per unit length and extreme strength.

Other problems such as space debris also need to be overcome.

Energy

When a force does work, energy is transfer from one form to another. If a body A exerts a contact force on a body B and does positive work, it follows that body B does negative work. Energy is lost by body A in doing positive work while energy is gained by body B having done negative work.

The unit of energy is the [N.m] or [J].

Forms of Energy

· kinetic energy

· potential energy – gravitational, elastic, electrostatic.

· thermal energy

· radiant energy

· chemical energy

· nuclear energy

On the microscopic scale, all forms of energy turn out to be either kinetic of potential energy

Even though energy may be transferred from one form to another the total amount of energy in the universe is constant. This is another important conservation law

The total energy in the universe is constant. This is the conservation of energy

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